Arrange compositor scrolling into scroll customization format

cc/layers/viewport.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/viewport.h"
 
 #include "base/logging.h"
 #include "cc/input/top_controls_manager.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
@@ skipping 132 matching lines @@
   if (scroll_delta.y() < 0)
     return true;
 
   if (TotalScrollOffset().y() < MaxTotalScrollOffset().y())
     return true;
 
   return false;
 }
 
 gfx::Vector2dF Viewport::AdjustOverscroll(const gfx::Vector2dF& delta) const {
+  // TODO(tdresser): Use a more rational epsilon. See crbug.com/510550 for
+  // details.
   const float kEpsilon = 0.1f;
   gfx::Vector2dF adjusted = delta;
 
   if (std::abs(adjusted.x()) < kEpsilon)
     adjusted.set_x(0.0f);
   if (std::abs(adjusted.y()) < kEpsilon)
     adjusted.set_y(0.0f);
 
   return adjusted;
 }
@@ skipping 22 matching lines @@
 
 LayerImpl* Viewport::InnerScrollLayer() const {
   return host_impl_->InnerViewportScrollLayer();
 }
 
 LayerImpl* Viewport::OuterScrollLayer() const {
   return host_impl_->OuterViewportScrollLayer();
 }
 
 }  // namespace cc